Harmonic control for recording and reproducing sound



July 23, 1935. J. H. HAMMOND, JR 2,008,708

HARD/IONIC CONTROL FOR RECORDING AND REPRODUCING SOUND Original Filed Oct. 14, 1931 11v VENTOR A TTORNEY g,

Patented July 23, 1935' HAEMONIC CONTROL roansooaomo C AND REPRODUCING .SOUND John Hays Hammond, J r., Gloucester, Mass.

Application October 14 19 1-, serial No. 568,690

Renewed October-12,1933, 1 18 Claims. (01. lief-100.4)

This invention relates to sound recording and reproducing systems, and more particularly to an improved system for controlling the harmonics in accordance with the sound intensity.

The invention relates particularly to a means for accentuating the high frequencies when the input signal is small, and for suppressing them when the input signal is large. In this way it is possible, when the music is soft, to bring out the overtones and thus prevent a decrease of quality which might otherwise occur, due to the fact that the high frequencies at low intensities become so weak that they are practically inaudible. At high intensities, the reverse action is desirable, as the high frequencies then become very penetrating and cause the music to sound harsh and metallic, so that it is necessary to suppress the overtones when the music is loud.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which the figure of the drawing illustrates diagrammatically the system as applied to the recording and reproducing the sound.

In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring more particularly to the accompanying drawing, a microphone I0 is connected through a transformer l l to one side of a doublepole, double-throw switch l2, the other side of which is connected to the pick-up I3 of a phonograph M, on the turntable of which is shown a standard phonograph .record IS.

The blades of the switch l2 are connected to the input circuit of a space discharge amplifier l6,.the output of which is connected through a transformer I! to two filter circuits l8 and I9, the formerbeing a high pass filter adapted to pass the overtones or harmonics of the applied speech or music, and the latter being a low pass filter adapted to pass thefundamental tones. The filter 1-8 is'connected through a potentiometer 2| to the input "circuit of a space discharge amplifier 2'2','theoutput circuit of which is connected through a transformer 23 to the input circuit. of a second space discharge amplifier 24;. .The out:

put circuit of this amplifier is connected through a transformer 25 to theinputcircuit of .a space discharge device-26, I a. j

The filter l-9- is connected through a.- trans-, former 21 to the input circuit of a space, discharge amplifier 28, the output circuitof which is connected through a transformer 28 toith'e inputcircuit of a space discharge device 31'. In. cluded in the plate circuits 'of the devices 16 and 3!, is the primary of a transformer 32,. the; secondary of which is connected to the input. circuit of a push-pull amplifier 33. The output circuit of this amplifier 33includestheprimary of a transformer 34 which isprovidedwith two secondarywindings, 34a and 3.41). Winding 34a. is connected to the blades, of a double-pole dou-' ble-throw switch 35, and winding 34b is connected .to a potentiometer 36 which is connected through a transformer 31 to a rectifier circuit 38. The output circuit of this rectifier. is connected through a reversingswitch 38a toresistanoe 39. This resistance is in the input circuit of two space discharge devices 40. These devices are supplied with filament and plate current from a source of A. C. through a transformer 4|. The output circuit of the devices 40 is connected to the winding of asolenoid 42, which is arranged to operate the potentiometerjl. V i 7 One side of the switch 35 is connected through a transformer 43 to'a loud speaker 44. The other 'side of this switch is connected. to an engraving mechanism 45 used for engraving a sound record on a record disk 46, which is driven by a phonograph mechanism contained in a casing 41. The engraving mechanism,..45 is slowly fed across the disk 46 as it rotates, by means of a mechanism contained in the casing, which is of well'known and standard construction.

In the operation of this system, with the switches l2 and 35 thrown to the left'fiand the switch 38a to the right, the speech or music is picked upby the microphone and passes through the transformer II and switch I2 to the amplifier 16, the output of which passes through the transformer I! to the filter cir cults l8 and IS. The high frequency currents pass through the filter l8 and the potentiometer 2| and are amplified by the amplifiers 22 and 24, and the low frequency currents pass through the filter I9 and the transformer 21 and are amplified by the amplifier 28. The outputs ofthe. am! plifiers 24 and 28 are then combined by the cir- S PATENTDFFICE cuits, including devices 26 and 3| and transformer 32. The energy passing through the transformer 32 is then amplified by the push-pull amplifier 33.

Part of the output from amplifier 33 passes through secondary 34b of the transformer 34, potentiometer 36 and transformer 31, and is rectified by the rectifier circuit 38. The output of this, circuit then passes through resistance 39 in the direction of the arrow, thereby building up a potential difference across this re-= sistance which is proportional to the output energy of the push-pull amplifier 33, which in turn is proportional to the total input energy of the system. With increased signal, therefore, this causes an increase of negative bias on the grids of the devices 40, thus increasing their internal impedance and decreasing their output current. In this way the current flowing through the winding of the solenoid 42 is decreased, allowing its core to move downward, thus de creasing the amount of high frequency energy picked up by the potentiometer 2|.

When the input signal strength is weak, however, the current fiowing through the resistance 38 will be small and the bias on the grids of the devices 40 will be low, thereby causing greater current toifiow through the solenoid 42, which in turn will move the core of this solenoid upward, thereby increasing the energy picked up by thepotentiometer 2| which increases the proportion of the high frequency energy fed to the amplifier 33. Y

The remainder of the output of the amplifier 33 passes through the other secondary of the transformer 34, and thence through the switch 351t0 the engraving mechanism which engraves ,a record of the music or speech on the record disk 46, in a well known and standard manner. This disk may then be used as a master for making any desired number of commercial records.

,Should itbecome desirable to increase the intensity of the harmonics with increase of signal the switch 38a is thrown to the left, thus causing the current from the rectifier circuit 38 to 'flow through the resistance 39 in the opposite direction to that shown by the arrow. With increase of the input signal strength this current will then cause a decrease of negative bias on the grids of the devices 40, thus decreasing their internal impedance and increasing their output current. This will cause an increase of current in the winding of the solenoid 42 which will cause its core to move upward, thus increasing the amount of high frequency energy picked up by the potentiometer 2|. With a decrease ofinput signal strength a reverse action will take place causing less energy to be picked up by the potentiometer 2 I.

When the system is to be used for the reproduction of music, the switches 12 and 35 are thrown to the right. Energy is then fed to the system from the pick up device l3 of the phonograph l4.' The operation of the system from here on to the switch 35 is identical to that already described in connection with recording. The energy from the amplifier 33 in this case, passes through the transformer 43 and is reproduced as speech or music in the loud speaker 44 in the usual manner.

It is thus seen that this system provides a means for accentuating the overtones when the total volume ofsound is small, and for suppressing these overtones when the volume of sound is great.

Although only one of the various forms in which this invention may be embodied has been shown herein, it is to be understood that the invention is not limited to any specific construction, but may be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

l; A system for producing sound from a sound record comprising in combination with an electrical transducer, a plurality of channels respectively adapted to pass currents of different frequencies, means for combining the output of the diiierent channels and means controlled by the amplitude of the combined output for controlling the relative proportions of the total energy passed through the respective channels.

2. A system for producing sound from a sound record comprising in combination with an electrical transducing system, a plurality of channels respectively adapted to pass currents of different frequencies, means for combining the output of the different channels and means controlled by the amplitude of the combined output for controlling the transmission characteristics of one or more of said channels.

3. A system for producing sound from a sound record comprising in combination with an amplifier a plurality of channels adapted to select and separately amplify currents of different frequencies, control means associated with one of said channels for controlling the proportion of the applied signal to the signal transmitted therethrough, means for combining the energy transmitted to all of said channels and means controlled by the combined energy for operating said control means.

4. In a system for producing sound from a sound record, an electrical transmission system adapted to translate between sound energy and mechanical energy comprising channels having means for selecting different frequency ranges, one of said channels having a control associated therewith for varying the relative intensity of the signals transmitted therethrough, means for combining the signals transmitted through all of said channels and means for operating said control in accordance with said combined energy.

5. In a system for producing sound from a sound record, an electrical transmission system for transducing between sound energy and mechanical energy which comprises a pair of transmission circuits, filters associated With each of said circuits and adapted to separate the energy into fundamental tones and harmonics respectively, means for combining the energy transmitted through both of said circuits and means operated in accordance with the combined energy for controlling the ratio of the harmonics inversely as the strength of said output signal whereby the effect of the harmonics is diminished as the output volume increases.

6. A sound system utilizing a sound record comprising in combination at least two channels, means for causing the first of said channels to pass fundamentals of the sound only, means for causing a second of said channels to pass harmonies of the sound only, and means controlled by the sound for governingthe relative volume of the sound passed through said channels.

7 A sound system utilizing a sound record comprising in combination at least two channels, means for causing the first of said channels to pass fundamentals of the sound only, means for causing a second of said channels to pass harmonies of the sound only, means for combining the energy transmitted by all of said channels record comprising in combination with an elec-' trical transducer, a plurality of channels respectively adapted to pass currents of different frequencies, means for combining the output of the different channels and means controlled by the amplitude of the combined output for controlling the relative proportions of the total energy passed through the respective channels.

9. A system for recording sound on a sound record comprising in combination with an electrical transducing system, a plurality of channels respectively adapted to pass currents of diiferent frequencies, means for combining the output of the different channels and means controlled by the amplitude of the combined output for controlling the transmission characteristics or one or more of said channels.

10. A system for recording sound on a sound I record comprising in combination with an amplifier, a plurality of channels adapted to select and separately amplify currents of different frequencies, control means associated with one of said channels for controlling the proportion of the applied signal to the signal transmitted therethrough, means for combining the energy transmitted to all of said channeis and means controlled by the combined energy for operating said control means.

11. In a system for recording sound on a sound record, an electrical transmission system adapted to translate between sound energy and mechanical energy comprising channels having means for selecting different frequency ran es, one of said channels having a control associated therewith for varying the relative intensity of the signals transmitted therethrough, means for combining the signals transmitted through all of said channels and means for operating'said control in accordance with said combined energy.

12. A sound system for recording on a sound record comprising in combination at least two channels, means for causing the first of said channels to pass fundamentals of the sound only, means for causing a second of said channels to pass harmonics of the sound only, and means controlled by the sound for governing the relative volume of the sound passed through said channels.

13. In a system utilizing a sound record, a first amplifier, a second amplifier, first and second paths between said amplifiers, said first path including a low pass filter for passing substantially fundamentals only, said second path including a high pass filter for passing substantially harmonics only, a double rectifier fed by said second amplifier, a circuit including a biasing resistance and a reversing switch fed by said double rectiher, a potentiometer in said second path, a solenoid for operating said potentiometer, a second double rectifier including a pair of three-element tubes, a source of alternating power current feeding said solenoid through said second double rectifier, the control electrodes of said second double rectifier being connected to said biasing resistance, whereby the strength of the signal in the output of said second amplifier determines the setting of said potentiometer and the position of said reversing switch determines whether the harmonics passed through said second path increase or decrease with increase in signal strength.

14. In a system for translating sound energy including a sound record, a pair of transmission channels adapted respectively to pass fundamentals and harmonics of the sound being translated, means controlled by the sound energy to vary the relative transmission characteristics of the channels, whereby the ratio of harmonics to fundamentals is varied, and reversing means associated with said first means to reverse said ratio for causing the harmonics to be accentuated or suppressed in accordance with an increase in sound energy.

15. In a system for translating sound energy including a sound record, a pair of transmission channels adapted to pass diiferent frequency components of the sound energy, means controlled by the sound energy to vary the relative transmission characteristics of said channels, whereby the ratio of the difierent frequency components is varied, and reversing means associated with said first means adapted to reverse the variation of said ratio with respect to the sound energy being translated.

16. The method of translating sound energy to or from a sound record which comprises separating the fundamentals and harmonics, and changing the ratio therebetween as a function of the sound energy.

17. The method of translating sound energy to or from a sound record which comprises increasing the ratio of higherfrequencies to lower frequencies with decrease in sound volume, decreasing the ratio of higher frequencies to lower frequencies with increase in sound volume, and causing said changes to be made automatically in accordance with the changes in sound volume.

18. In a sound record system, a pick-up device, a plurality of parallel channels fed thereby, a translating device fed by the combined output of said channels, and means responsive to the total signal transmitted to vary the transmission efficiency of one of said channels.

JOHN HAYS HAMMOND, JR. 

